Stabilized motor fuel



Patented Apr. 14, 1953 STABILIZED MOTOR FUEL Delaware No Drawing. Application April 7, 1950, Serial No. 154,721

(Cl. id-69) 6 Claims.

This invention relates to the stabilization of hydrocarbon fuels normally susceptible to deterioration. More particularly, my invention relates to the prolongation of the useful life of gasoline and other fuels for internal combustion engines by inhibition of attack by oxygen.

Hydrocarbon fuels for use in internal combustion engines are characterized by a diversity of hydrocarbon types. For example, typical automotive fuels contain olefins, naphthenes, straight and branched chain aliphatic hydrocarbons, and some aromatics, while typical aircraft fuels contain a lower proportion of olefins. During the refining, manufacturing and blending processes, and during subsequent storage and handling operations, it is unavoidable that these fuels or their ingredients, such as cracked blending stocks, or the highly olefinic stocks for reforming and alkylation, are brought into contact with oxygen. The result of such. contact is the formation, by oxidation or polymerization or a combination thereof, of gummy materials which interfere with the efiicient utilization of said fuels in the engine. Automotive gasolines are, in general, more susceptible to this type of degradation by oxygen than finished aircraft fuels.

In recent years a similar problem of degradation of fuels for use in compression ignition engines has become prominent. The percentage of cracked stocks in such fuels has increased, resulting in a higher olefin content, with a resultant increase in susceptibility to gum formation on exposure to oxygen. The presence of such gummy materials interferes with the normal operation of the fuel filters and injectors in compression ignition engines, thus lowering the I efficiency of the engine.

Because of the specifications imposed on fuels by the rigid requirements of present day engines. particularly aircraft engines, it is essential that any material capable of protecting such fuels against deterioration by oxygen be effective in extremely small quantities, on the order of one pound of additive per five thousand gallons of fuel, so that secondary problems do not arise through their use.

It is therefore an object of my invention to provide means for protecting such hydrocarbon fuels which deteriorate in or are affected adversely by oxygen. It is a further object of my invention to provide a class of substances which prevents the formation of gummy oxidation and polymerization products of unstable hydrocarbons on contact with oxygen. Another object of my invention is to provide means for stabilizing hydrocarbon fuels for internal combustion spark iii and compression ignition engines during the manufacturing, handling and storage of such fuels prior to their use. A still further object of my invention is to provide a finished gasoline, containing tetraethyl lead which will retain, during blending, storage and use, the performance characteristics inherent in the fresh fuel mixture. Still further objects of my invention will appear from the description of my invention as hereinafter disclosed.

The above objects can be accomplished by practicing my invention which comprises adding to hydrocarbons a small proportion of a substance derived from the class of N-cyclohexylaminodiphenylamines.

In general the substances which comprise my invention can be described by the general formu a wherein X is either hydrogen or alkyl, and the number of alkyl substituents, X, on each cyclohexyl radical varies from 0 to 2, inclusive, and n is an integer from 1 to 2 inclusive. I have made the discovery that when compounds conforming to the abovedescribed formula are added insmall proportions to hydrocarbons which are normaily unstable in the presence of oxygen, the resistance of such hydrocarbons to the deleterious action of oxygen is markedly improved. In particular, hydrocarbon fuels in the gasoline boiling range and higher are benefited by their presence.

The simplest members of the antioxidant materials of my invention are the (cyclo'hexylamino) diphenylamines. The embodiment of this example of the compounds of my invention which I prefer is 4-(cyclohexylamino)diphenylamine. A further embodiment of the compounds of my invention, wherein the antioxidant property is enhanced, comprises the di(cyclohexylamino)diphenylamines, wherein n in the above general formula is the integer 2. A preferred example of this embodiment of my invention is the compound 2,4-di(cyclohexylamino)diphenylamine.

In addition to possessing the antioxidant func tion, a material acceptable for commercial use also possess the proper balance of solubility in the fuel to be protected and other fluid media with which such inhibited fuel may come in contact. For example, gasoline blending stocks may be treated with aqueous solutions during various steps of the refining process. Likewise, finished gasoline is commonly stored in tanks containing more or less water. Therefore, an antioxidant additive in the fuel, to remain effective under such conditions, must be only sparingly soluble in water, and sufficiently soluble in the hydrocarbon fuel to maintain an effective inhibiting concentration of additive. It is thus within the scope of my invention to incorporate in the (cyclohexylamino)diphenylamine molecule of the compounds of my invention certain groups which, while having no enhancing effect on the antioxidant property, increase the hydrocarbon solubility, above that ascribable to the cyclohexyl group, and decrease the water solubility thereof. I have found that an effective method of accomplishing this purpose is the substitution of alkyl radicals in the cyclohexyl group of the antioxidants of my invention, the position of said substituents on the cyclohexyl ring being largely immaterial, and dictated by the availabilityv and cost of the required raw materials for the manufacture of such substances. Thus, preferred examples of the compounds of my invention so-modified to exhibit the proper solubility relationship for certain uses include the (methylcyclohexylamino) diphenylamines, such as the (methylcyclohexylamino) diphenylamines and the (dimethylcyclohexylamino) diphenylamines, in which the methyl radicals are disposed in the ortho-, meta-, and para positions of the cyclohexyl radical.

The absorption of oxygen by hydrocarbon fuels is measured directly by the standard method of the American Society of Testing Materials for determination of the oxidation stability of gasoline (induction period method). ASTM designation: D525-46, as fully described in Part lII-A, ASTM Standards for 1946. According to this method the induction period is the period during which there is no drop in pressure, indicating no absorption of oxygen when the test material is placed in a testing bomb maintained at a temperature of 100 C. with an initial pressure of 100 pounds per square inch gauge of oxygen. The induction period increase (I. P. I.) is the increase in the duration of this period caused by the addition of a protective substance, and is a direct measure of the protection afforded by such additive. Thus, the longer the I. P. I the more effective is the stabilizer. On the contrary, certain substances exert a pro-oxidant effect in which a negative I. P. I. is obtained, that is, the

duration of the induction period, or period of no to 2 per cent of the gasoline.

It is well known in the art of protecting gasoline from oxidation that the susceptibility to oxidation of gasolines varies significantly with different types of gasolines. Furthermore, it is likewise well known that the efficiency of any antioxidant, and the minimum concentration required, will vary greatly from gasoline to gasoline. Therefore, in order to show the general applicability of the compounds of'my invention to the solution of this problem, and at the same time not present in detail the large amount of data so obtained, I have listed in Table I the average I. P. I. obtained with a sensitive test asoline.

The utility of the compounds of my invention in preventing deterioration of hydrocarbon fuels by the action of oxygen is not impaired by the co-presence of other additives which may be added thereto. Thus, tetraethyllead and halogen-containing scavengers therefor, commonly present in finished gasoline, will not interfere with the protection afforded by my antioxidants. In fact, it is usually desirable to add one of my antioxidants to gasoline prior to blending the gasoline with the tetraethyllead composition, to protect the gasoline during the blending operation. The protection so-provided to the finished fuel is thereupon useful during subsequent handling, storage and use of the fuel. Thus, the induction period of a sensitive gasoline containing 3 milliliters of tetraethyllead per gallon was determined to be 150 minutes by the above-described test procedure, while this same gasoline composition to which had been added 3 milligrams per gallon of 4-(cyclohexylamino)diphenylamine was 510 minutes, a more than twofold increase.

The quantities of the compounds of my invention incorporated in the materials to be stabilized are not critical and depend largely upon the type of material being stabilized and the conditions under which the exposure to oxygen occurs. For example, with gasolines, under normally encountered storage or manufacturing conditions the compounds of my invention are preferably employed in concentrations between the limits of approximately 0.1 and 15 milligrams per 100 milliliters of material to be stabilized. Thus, my compounds can be satisfactorily employed in a wide range of concentrations, and I do not intend that my invention be restricted to the specific quantities mentioned herein.

I have disclosed a number of prefered embodiments of my invention and illustrated several means whereby protection can be afforded to hydrocarbon fuels sensitive to attack by oxygen. My invention is not intended to be limited to the specific embodiments of my invention herein or to the means described herein for obtaining the advantages possible in employing my compounds, as other methods of practicing my invention will be apparent to those skilled in the art I claim:

1. A new composition consisting essentially of a petroleum hydrocarbon motor fuel for internal combustion engines normally tending to deterirate in the presence of oxygen and a (cyclohexylamino)diphenylamine, present in an antioxidizing amount, said (cyc1ohexylamino)diphenylamine having the general formula wherein X is selected from the group consisting of hydrogen and alkyl, n is an integer from 1 to 2 inclusive, and the number of alkyl substituents on each cyclohexyl radical varies from 1 to 2, inclusive.

2. A new composition stable to oxidation consisting essentially of a petroleum hydrocarbon fuel for internal combustion engines, an antiknock substance comprising tetraethyllead, and

a (cyclohexylamino)diphenylamine having the general formula wherein X is selected from the group consisting of hydrogen and alkyl, n is an integer from 1 to 2 inclusive, and the number of alkyl substituents on each cyclohexyl radical varies from 1 to 2, inclusive, said (cyclohexylamino)diphenylamine present in an antioxidizing amount.

3. The composition of claim 1 in which the antioxidant is a mono- (methylcyclohexylamino) diphenylamine.

4. The composition of claim 1 in which the antioxidant is a di-(methylcyclohexylamino)- diphenylamine.

5. The composition of claim 1 in which the integer n is 1.

6. The composition of claim 1 wherein the integer n is 2.

EUGENE F. HILL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,048,823 Semon July 28, 1936 2,115,473 Semon Apr. 26, 1938 2,256,189 Bogemann et a1. Sept. 16, 1941 

1. A NEW COMPOSITION CONSISTING ESSENTIALLY OF A PETROLEUM HYDROCARBON MOTOR FUEL FOR INTERNAL COMBUSTION ENGINES NORMALLY TENDING TO DETERIRATE IN THE PRESENCE OF OXYGEN AND A (CYCLOHEXYLAMINO) DEPHENYLAMINE, PRESENT IN AN ANTIOXIDIXING AMOUNT, SAID (CYCLOHEXYLAMINO) DIPHENYLAMINE HAVING THE GENERAL FORMULA 